Disposable trays of fibre material coated with a removable film layer

ABSTRACT

A method for producing a compression-moulded tray of fibre material, said tray being formed of fibre material in a compression method, from a suspension of mechanical pulp of cellulose. The formed tray is formed by press-drying using heat to a dry content of 80-95%, preferably 90-95%, and the fibre material of the formed tray has a density in the order of 400-650 kg/m3. The inside of the tray is provided with a protective barrier, said barrier being removable.

FIELD OF THE INVENTION

The present invention relates to disposable trays with coated with afilm layer. More specifically the present invention relates to acompression-moulded tray of fibre material coated with a removable filmlayer. The present invention also relates to a method of producing suchfilm-coated trays.

BACKGROUND

The handling of foodstuff put very high demands on the packaging. Theymust meet the hygienic requirements, i.e. bacteria and flavouring agentsshould not be able to migrate through the packages to and from thesurrounding environment. In some cases the tray should even be gastight, i.e. for chilled food for long storage or fresh meat in modifiedatmosphere. They should have enough strength to resist the handlingduring storage and transport.

It has become more and more common with ready-cooked food dishes, and inaddition to serving as a package for storage of the foodstuff, there arealso requirements that it should be possible to put the packagesdirectly into a microwave oven or a conventional oven for cooking orheating of the food dishes.

Packages in the form of aluminium forms are nowadays used to a greatextent. They resist conventional ovens, but the disadvantages are thatthey become very hot and sometimes even impossible to hold in yourhands. Aluminium forms are also very fragile and cannot resist a greatload. Moreover, they cannot be put in a microwave oven

Another common type of packaging is a tray of foamed, vacuum-formed orcasted polyester. An essential disadvantage with solid or foamed plastictrays is that they cannot be put in a conventional oven, since they willthen melt. The same will thing also happens with solid plastic traysthat are common in convenient stores nowadays.

In U.S. Pat. No. 6,245,199 a method of mould-casting trays, where thestarting material is a suspension comprising cellulose fibres, isdescribed. Moulds are dipped, from above, in a bath of the suspension,after which the compression-moulding is performed under heat.

The choice of material suggested in the U.S. patent for the forming pulpis however not optimal for the manufacturing process and results in aformed tray lacking in function. Moreover, there is no specification ofthe pulp, only how the machinery works. Also, the describedmanufacturing process and assembling have some flaws like low anduneconomical production rate, large areas that have to be well sealedagainst air leakage. Air pressure from the back of the moulds demandsextremely good rigidity as the tool tolerances, when in contact, areless than 1 mm. This results in bad reproducibility and a decreasedquality of the trays. The tools used may also cause crushing ofcellulose at certain locations on the tray.

It is known to form trays from a starting material in the form of apaper web normally comprising multiple layers. The forming is performedby stretch-forming the web using a pressing tool. One example of amethod of this kind is described in EP 1 160 379-A2. This documentsuggests the use of a paper web that has been improved as regards itsstretchability and elasticity, properties that are important when thematerial is to be stretched and deformed in order to form it.

The forming of trays from a material web is however associated with anumber of disadvantages. Even if the flexibility and elasticity havebeen improved, as is indicated in EP 1 160 379-A2, there are stilllimitations with regard to its flexibility and elasticity, which in turnresults in limitations in the formability. It is impossible to producedeep trays or multi compartment trays from a web, since it is impossibleto form a tray or bowl from a flat sheet even if you have moistened itup to water a content 50%. Furthermore, undesired folds are formed whendepressions are made in the material web in connection with the formingof the trays. The web used may even break. An essential disadvantagewith the trays according to EP 1 160 379-A2, is that the formed traysare stretched and that they have built-in tensions that may cause theformed trays to be deformed when exposed to stresses in the form ofchanges in temperature or when exposed to moisture or dampness.

Tough environmental demands are also put on the packaging, i.e., as torecycling, composting or incineration of used packages. The demands ondisposable trays and their film coating are very different, andtherefore they also constitute very different waste disposal problems.Ideally, said tray and film layer should be separated beforerecycling/incineration. However, with the present film-coated disposabletrays with layers, separation of the film layer is impossible or atleast difficult. For environmental reasons it would therefore be desiredto have disposable trays where said film layer could easily be removed.

ACCOUNT OF THE INVENTION

By the present invention, a disable tray with a considerably improvedfunction and which is easily recyclable compared to previously knowndisposable trays has been achieved. The present invention specificallytargets the problem of recycling, composting or incineration of usedtrays.

The present invention solves the above-mentioned problems using acompression-moulded tray of fibre material coated with a removable filmlayer. The compression-moulded fibre tray and suitable films for thecoating are described in the co-pending application PCT/SE2007/050190belonging to the same applicant.

It has been discovered that when said fibre material and said films areused for the coating film layers, a tray having a removable film layercan be produced. The film, applied onto the compression-moulded fibretray according to the methods described in PCT/SE2007/050190, is made bymaking a small portion of the tray breakable by hand force.

Said breakable portion is suitably located at a rim or an upper part ofan edge of the tray. The breakable portion is preferably kept small asto maintain the overall stability and properties of the tray.

The portion of the rim/edge may for example be made breakable bypunching a small area of the rim/edge such that a well-defined breakableportion is produced. Such a well-defined breakable portion may also beachieved by making a small portion of the rim/edge has a reducedthickness.

When applying force on said weakened portion of the rim/edge, the fibretray will break at the edges of said well-defined area of the rim/edge,leaving it connected to the rest of the tray only via the film layer.Due to the constitution of the fibre tray and the film coating, whenpulling onto the broken part of the tray, said film is easily peeled offthe fibre tray by hand force. The fibre tray can then be composted orburnt, and the film be burnt, or disposed of in any suitable way.

The present invention also relates to a method of producing suchfilm-coated trays with removable film layers.

The tray according to the invention is characterised in that the tray ina compression method is formed from a suspension of a fibre material ofcellulose, comprising at least 75% virgin fibre-based mechanical pulpfrom the group TMP, CMP, CTMP, cTMP, HTCTMP and mixtures thereof, and inthat the formed tray has been formed by press-drying using heat to a drycontent of 90-95%, in that the fibre material of the formed tray has adensity in the order of 400-650 kg/m³, and in that the tray on itsinside is coated with a protective barrier.

By choosing the mentioned kind of virgin fibre-based mechanical pulp ofcellulose as fibre material in the tray, several advantages areobtained. Fibres of mechanical pulp are stiffer than any other type ofcellulose pulp, such as chemical pulp or pulp that is partly or fullycomprised of recycled fibre. This means that the tray formed frommechanical pulp is more resistant to deformation. The remaining residuesof natural resins in the mechanical pulp also causes the formed tray tobe self-hydrophobing, which is important in order for the tray tomaintain its shape and strength even in humid environments. Press-dryingalso introduces built-in stress into the product which gives therigidity at a low basis weight. Said stress is evenly distributed andresults in an additional contribution to the stability, due to the factthat the fibres have been forced to a shape under heat and pressure intoa fibre network. Inner stress yields in this case a better strength andstability. The hydrophobic fibres also prevent future penetration ofwater, which in turn also promotes long-lasting strength and stability.

The formed tray has been formed by dry-pressing under heat to a drycontent of 80-95%, preferably to a dry content of 90-95%. This resultsin the forming of very strong hydrogen bonds between the individualfibres, and in the obtaining of a tray with high resistance tocompressive stress.

Press-drying is preferably performed at 250-280° C. This temperatureinterval results in a good production efficiency. Higher temperaturesmay result in burning of the fibre material.

By hard-compressing the fibre material in the compression method to adensity in the order of 400-650 kg/m³, a tray with high stiffness thatcan resist very high compressive loads is obtained. When compressing tothis density, the fibre material is strong enough for use as food traysand will have a very good surface for lamination of various plasticfilms as PET (polyethylene terepthalate), PA (polyamide), PP(polypropylene), and PBT (polybutylene terephthalate). Both higher andlower densities will create lamination and tightness problems. Thecorrect smoothness of the surface is a very crucial property and is verymuch linked to the density of the tray. If for instance the density istoo low (<400kg/m³), the surface will be too rough, causing pinholes inthe lamination film. If the density is too high (>650 kg/m³), thesurface will be too smooth and the lamination film will notadhere/anchor well enough to the fibres.

According to a suitable embodiment, the invention is furthercharacterised in that said mechanical pulp comprises at least 75% CTMP.

According to one embodiment, particularly intended for the use as a trayfor foodstuff, such as ready-cooked food dishes, the invention ischaracterised in that said protective barrier is constituted by anaqueous plastic emulsion.

A plastic emulsion of the above-mentioned kind is sprayed on the fibretray and subsequently “polymerised” (forming a film during drying justlike water-based paint) to a plastic film.

According to one embodiment, the invention is characterised in that saidfilm of PET, PA, PP, PBT or similar is applied on the formed traythrough heat-lamination.

The film can be clear, transparent and/or coloured. Normally, a blackfilm is preferred. A black film greatly facilitates the heat-laminationto the formed fibre tray, since the added heat to a higher degree isabsorbed by a black material than by other colours. By using a blackfilm, it is thus possible to achieve a sufficiently high and evenlamination temperature

PET has unique properties which makes is particularly suitable for theintended application purpose. In connection with the lamination, the PETfilm changes from an amorphous to a crystalline molecular structure. Incrystalline form, the PET can resist both heating and freezing. PET hasin crystalline form a softening temperature of approximately 220° C.,which makes it resist heating in a conventional oven. Moreover, PET incrystalline form is gas-tight and protects well against migration ofbacteria and flavouring agents.

In some cases PA, PP, PBT alone or in combination with EVOH (ethylenevinyl alcohol copolymer) may be more suitable. The choice of filmmaterial depends on what degree of air-tightness is needed and how thefood is processed inside the tray, will the tray be top sealed withanother film or not. If for example an air-tight tray is desired, i.e.suitable for chilled food for long storage, a co-extruded film with EVOHis suitably used, as this is one of the most air-tight compounds afteraluminium. For frozen food there are lower demands, and a PET or PA filmis sufficient and may suitably be used.

PET in crystalline form can also resist vapour sterilisation(autoclavation), which is performed under high vapour pressure and at atemperature of 125-130° C. All polymers are not suitable for this typeof sterilisation. During vapour sterilisation, the material gets incontact with vapour, which is something that not all polymers canresist, such as for example PVC, polyethylene, and polyamide.

Amorphous PET, so-called APET, has a very high tensile strength and cantherefore be pressed down into very deep trays that are to be laminated.PET in crystalline form, so-called CPET, has also a high wear resistanceand resistance to chemicals.

PET is also a very suitable material as regards the environment. PET iseasy to recycle from used trays. Due to the fact that PET has a veryhigh tensile strength, it is easy to separate PET in large flakes fromthe rest of the tray. PET is also suitable for incineration.

According to one embodiment, the invention is characterised in that thetray, by the press-drying, has been provided with a smooth surfacestructure without protruding fibres. By this, the risk of so-called“pin-holes” is eliminated.

According to one embodiment, the invention is characterised in that thetray has a planar bottom and side walls that are straight to saidbottom. This facilitates the lamination to the plastic film. The use ofstraight side walls in relation to the bottom has been made possiblethanks to the fact that the tray according to the invention, in contrastto other known trays for use as food package for ready-cooked dishes,has a considerably higher resistance to compressive load. Previouslyknown trays are usually provided with special reinforcing bumps forobtaining an acceptable load strength. Irregularities in the form ofreinforcing bumps results in a decreased lamination of the film.

According to one embodiment, the invention is characterised in that theopening of the tray is surrounded by an outwardly extending and withsaid bottom parallel and completely smooth rim. This has also been madepossible by the fact that the tray according to the invention is builtby material that is stiff and resistant to high compressive loads. Asmooth rim facilitates the sealing of the tray with a lid.

According to one embodiment, the invention is characterised in that thetray is formed from a suspension of fibre material having a pH between 6and 8.5, preferably between 7 and 8. It has been shown the tray is muchstronger at a pH close to a neutral pH value. This is believed to becaused by the formation of stronger hydrogen bonds between the fibres atthis pH value.

According to one embodiment, the invention is characterised in that thefibre material of the tray has been treated with a hydrophobing agent.

According to one embodiment, the invention is characterised in that saidhydrophobing agent is constituted by AKD (alkyl ketene dimer) or ASA(alkyl succinic anhydride). These hydrophobing agents is suitable as itis resistant to both freezing and heating.

According to another aspect, the present inventions provides a method ofmanufacturing the above-mentioned trays.

According to another aspect, the present inventions provides a method oflaminating films on a fibre material. Said method enables lamination ofvarious films to a fibre material. The method is particularly usefulwhen using a film exhibiting increased E-modulus when stretched, such asPET, PA, and PBT films, since this will yield a very even film. Otherfilms are also suitable, but are then preferably used in combinationwith another film.

DESCRIPTION OF THE DRAWINGS

The invention will in the following be described more in detail withreference to an embodiment, which is shown in the appended drawing. Inthis drawing, FIG. 1 shows an example of a tray according to theinvention seen from above; FIG. 2 shows a cross-section along the lineII-II; FIG. 3 shows a perspective view from above of the backside of atray according to the invention, where the rim/edge of the tray featuresa punched portion (hatched line); and FIG. 4 shows a horizontal sideview of the rim/edge of a tray according to the invention, where saidrim/edge features a portion having a reduced thickness.

DESCRIPTION OF EMBODIMENTS

The tray shown in FIG. 1 has a planar bottom 1 and from that straightside walls 2, which surround an opening 3. The opening of the tray issurrounded by an outwardly extending and with said bottom parallel andcompletely smooth rim 4. The tray has an inside 5 and an outside 6. Thetray is formed from a suspension of a fibre material of mechanical pulphaving a pH between 6 and 8.5, preferably between 7 and 8. It has beenshown that the tray becomes stronger when formed from a fibre suspensionhaving an essentially neutral pH value. The inside of the tray is coatedwith a film 7 of PET or another film as mentioned above. Thecompression-moulded fibre tray has been denoted by 8.

FIG. 3 shows a perspective view from above of the backside of a bottom 1of the tray 8 according to the invention, where a rim/edge 4 of the trayfeatures a punched portion 9 (hatched line). The punching may beperformed by any conventional means used before or after thefilm-coating procedure.

FIG. 4 shows a horizontal side view of the rim/edge 4 of the tray 8according to the invention, said tray being coated with a film 7, andwhere said rim/edge features a portion 10 having a reduced thickness.The reduction of thickness of said portion of the rim/edge thickness mayfor example be achieved by compressing said portion before or after thefilm-coating procedure.

The manufacturing of the fibre tray according to the invention is inprinciple performed in the following way.

Dewatering trays having a shape that corresponds to that of the shape ofthe tray to be manufactured is immersed into a bath in the form of asuspension of mechanical pulp. The fibre material suitably comprises atleast 75% CTMP. The fibre material of CTMP has the advantage that isself-hydrophobing and results in a more porous and thus moreair-permeable structure than for example ground pulp, which in turnimproves the forming in the dewatering trays. CTMP is also advantageousduring the subsequent lamination with PET, as air can more easily passthrough the more porous structure in a formed fibre tray of CTMPcompared to other mechanical pulps. The dewatering trays for a fibresuspension of CTMP suitably have a mesh size of 60 mesh or finer.

After the formation in the dewatering trays, the trays are transferredto a pressing tool where press-drying under heat and high compressivepressure takes place in one or several steps. Press-drying under heatshould be continued until the compression-moulded fibre tray has reacheda dry content of 80-95%, preferably 90-95%. In order to obtain a stifffibre tray, it is important that the press-drying under heat isperformed to the said dry content. It is not before this dry contentthat the desired strong hydrogen bonds between individual fibres aredeveloped.

Furthermore, the compressive pressure in the press-tools should be sohigh that the fibre tray gets a density in the order of 400-650 kg/m³.If the density is too low, the surface will be to rough, causingpinholes in the lamination film. On the other hand, if the density istoo high density, a very smooth surface is produced, and the film willnot glue/stick to the fibre material. It has been shown that a formedfibre tray having said properties gets particularly good properties foruse purposes, in which the tray is exposed to great stresses in the formof high compression loads, high heat under prolonged periods, freezing,as well as liquids and moisture. An example of a suitable applicationfield is packages for ready-cooked dishes, where the stresses of theabove-mentioned kind are present and where there are no known suitablesolutions that can withstand both conventional and microwave-heating,and still can be taken out from said ovens with bare hands.

According to one embodiment, a hydrophobing agent is added to the fibresuspension. The intention is that the formed fibre tray thus shouldbecome strongly water-repellent. Absorption of water would result in agreat reduction of the tray's resistance to loads. According to asuitable embodiment, the hydrophobing agent is AKD (alkyl ketene dimer).The advantage with this hydrophobing agent is that it is resistant toboth heating and freezing.

According to a suitable embodiment, the fibre trays are laminated ontheir inside with a film of PET. A film of PET is particularly suitable.PET has a high tensile resistance, which makes it possible to stretchthe film in connection with the lamination to the fibre tray without itbraking. When using a film of PET having a thickness of 50 μm, trayshaving a depth of at least 5 cm can be formed without problem.

The film is applied as a web over the pre-formed fibre tray and issucked down into the tray using vacuum, while the film is heated forlamination using heat radiation.

The PET film is suitably black, for the reasons described above. It mayalso be clear, transparent and/or coloured. The PET film is constitutedof amorphous polyester. The colouring is performed by a so-called masterbatch, comprising colour pigments in concentrated form, in connectionwith the extrusion of the film. During stretching of the film, inconnection with the lamination, the film is extended and the thicknessof the film will in a laminated state be less than 50 μm. During thelamination process, the amorphous structure is crystallised and istransformed into CPET, i.e. a crystalline polyester. A film of CPEThaving a thickness of approximately 10 μm is essentially gas-tight andbacteria-tight. CPET film has a low moisture absorption, high wearresistance and is resistant to chemicals. Depending on end use, otherfilms may be more suitable. When the tray needs a top film to protectthe food, it may sometimes be difficult to glue a film on CPET. In suchcases, a top film of PA/PP film is easier to glue/adhere to said tray.There is always a co-operation between different films and the choice oftop and lamination film must always be judged and tested individually.

The pressing tools for the press-drying are suitably completely smoothin order to achieve a surface structure on the formed tray that issmooth and without protruding fibres, which may give rise to “pin holes”in the plastic film during its lamination.

In the following, tests that have been performed on an embodiment in theform of a fibre tray of CTMP and a PET film laminated to said fibretray.

The tested trays have a very good surface finish, good stability andhigh heat insulation capacity, which make them well suited for e.g.heating of ready-cooked dishes in microwave and conventional ovens. Thegood heat insulation capacity makes it possible to hold the traycontaining the heated dish in the hand, without any risk of gettingburned.

The migration is very low, whereby the trays are well suited for directcontact with foodstuff. When packaged in a modified atmosphere, aplastic laminate having a low permeability is suitable.

The form stability of the trays makes them suitable for automatedhandling in filling and packaging machines.

The tests have been performed on the heat resistance of the trays,filled and unfilled, to verify that they can be used for serving hotfood and in for example airplanes. As is seen below, the tests show thattrays according to the invention have a very high heat resistance.

The trays have also been tested in respect of autoclavation andpasteurising, respectively, with good results. The tests have beenperformed with and without a plastic bag around the trays. The reasonfor using a plastic bag, is to simulate a tray sealed with a lid film,which should always be the case during autoclavation and pasteurising.

The trays have a very good stability and resist very high loads beforeany breakage has been observed.

In summary, it can be concluded that the trays are well suited for alarge number of applications, both for foodstuff and technical products.

Description of the Manufacturing Process

Reslushed or fresh CTMP is formed on a wire net or similar device (froma consistency of about 1% up to about 15%) to its desired tray shape.The formed tray is then dried between hot tools in several stages withthe help of vacuum and compressed air, to the desired dryness of about90%, which is suitable for imparting a sufficient rigidity to the tray.Additional hydrophobising agents and retention aids are added to thestock before dewatering in order to improve the production, since theretention aids speeds up the dewatering process and binds the finematerial (very small fibre fragments) to the fibre web. The performanceof the production is improved since a large part of the hydrophobingagents stick to the fine material, and the retention aids keeps saidfine material from being flushed out with the white water. The provisionof the barrier-coating or lamination takes place immediately after thetrays have been dried to about 90% dryness. The trays may be checkedwith a metal detector before delivery to the user, since metal fragmentsare completely forbidden in food trays for many reasons, e.g., it may beharmful to get sharp pieces if metal into your body and if metal piecesare put into a microwave oven, they can cause a fire

EXAMPLES

Tested Materials

Polyester-laminated fibre trays formed of CTMP from a suspension. Thedimensions of the trays were 173×117×30 mm.

Testing

Surface weight measurements were performed according to ISO 536:1995.Samples were taken from the bottom and the side walls of the trays.

Measurements of the thickness and density were performed according toISO 534:1998. Samples were taken from the bottom and the side walls ofthe trays.

Measurements of the tear strength were performed according to ISO1974:1990. Samples were taken from the bottom and the side walls of thetrays.

Absorption of Water

A. The weights of the trays were measured, after which the whole traywas submerged under water for 60 seconds. After drainage of the waterand drying in air for 1 minute, the tray was weighed again. The gain inweight was reported.

B. The weights of the trays were measured, after which they were filledwith 5 dl of water and were left to stand in room temperature for 24hours. After 1 minute (B1), and 15 minutes (B2) of drying time, the traywas weighed again. The gain in weight was reported.

Measurements of the compressive strength were performed betweenplane-parallel loading plates with a compression speed of 10 mm/minute.The maximal load capacity of the trays was measured on new trays,0-tests, and on trays after autoclavation.

Autoclavation was performed on 5 trays, each filled with 100 ml ofwater. The trays were autoclavated at different temperatures and times,both enclosed in plastic bags and without plastic bags.

The temperatures and times were 120° C. for 60 minutes, 100° C. for 45minutes, and 90° C. for 1 minute (pasteurisation), after which the trayswere dried in drying chambers at 50° C. for 1 hour.

1 tray from each temperature was compression-tested.

Tests of fire smoke was performed on 6 trays filled with lasagne. Thetrays were placed in a Regina Culinesse hot air oven from Husqvarnahaving a temperature of 225° C.±5° C. under 90 minutes. Any presence offire smoke was judged visually by two independent persons.

Empty trays were tested to control possible ignition in oven. Thetemperature was measured by infrared non-contact temperature meters. Ata surface temperature of 290° C., the underside of the trays wasdiscoloured, but apart from that, the trays were intact. No ignitionoccurred, which is in line with previous experience, namely that organicmaterial like cellulose does not normally self-ignite in temperaturesbelow 400° C. Kitchen ovens are also limited to 300° C. to preventself-ignition.

Result

Thickness Surface weight Density (μM) (g/m²) (kg/m³) Tray Bottom SideBottom Side Bottom Side 1 1168 748 581 456 497 609 2 1436 773 594 483414 625 3 1341 703 596 476 445 677 4 1474 805 626 526 425 654 5 1466 852633 523 432 614 6 1322 597 452 7 1346 591 439 8 1345 667 496 9 1332 654491 10 1143 594 520 Average 1337 776 613 493 461 636 Std. dev. 111.556.4 29.7 30.6 36.6 28.9

Tear strength (mN) Tear index (Nm²/kg) Tray Bottom Side Bottom Side 18290 5990 14.3 13.1 2 8060 4750 13.6 9.8 3 10600 8770 17.8 18.4 4 94204280 15.1 8.1 5 8490 5290 13.4 10.1 6 5450 9.1 7 6540 11.1 8 9330 14.0 97760 11.9 10  6380 10.8 Average 8032 5816 13.1 11.9 Std. dev. 1569.81769.8 2.5 4.0

The abbreviation Std. dev. stands for standard deviation.

Absorption of water A B-1 B-2 Tray g % g % G % 1 2.1 12.8 0.75 4.3 0.734.3 2 1.8 11.4 0.81 4.6 0.78 4.6 3 1.9 12.6 0.27 1.6 0.27 1.6 4 1.9 11.65 1.7 10.4 Average 1.6 11.8 0.6 3.5 0.6 3.5 Std. dev. 0.15 0.97 0.301.65 0.28 1.65

Compression to Maximum Load in N, Compression in mm

0-test Tray N mm 1 531 7.6 2 602 6.9 3 576 6.7 4 489 6.4 5 488 11.1Average 537.2 7.7 Std. dev. 51.2 1.93

After autoclavation 1 min. 90° C. N mm 567  6.7 With plastic bag 55312.0 Without plastic bag

After autoclavation 45 min. 100° C. N mm 572 8.8 With plastic bag 4279.3 Without plastic bag

After autoclavation 60 min. 120° C. N mm 573 9.9 With plastic bag 4937.1 Without plastic bag

Visual Judgment of the Fire Smoke

After a few minutes in the oven at a temperature of 225° C., the plasticbegan to come off at the edges of all trays. After 90 minutes, theoutside of the trays was slightly brown-coloured. No smoke could bedetected. The packaged foodstuff was relatively charred on the upperside.

Ignition Test

The surface of the tray became brown, but the rest of the tray remainedintact at 290° C. No ignition occurred.

In addition to the tests mentioned above, the above-mentioned trays werealso tested as to migration. Tests were performed according to ISOEN-1186-14, which is intended for migration-testing of plastics, thatwhen used, get in contact with fatty foodstuff. The test media wereconstituted by iso-octane and 95% ethanol.

Total Migration

Total migration Sample Media Test conditions (mg/dm², sample) Average 195% ethanol 6 h 60° C. −0.6; −0.5; −0.6 <1 1 iso-octane 4 h 60° C. −0.1;−0.4; −0.3 <1

The migration average is based on a triple analysis according toEN-1186. The accepted value of migration in packages for food is <10mg/dm².

The transmission of oxygen through the plastic film and the fibrematerial was measured according to ASTM D 3985-95 using a so-called“coulometric sensor”.

Oxygen-Transmission Result

Transmission of oxygen Sample Test conditions Area (cm²) (cm³/m²/day)Average 1 23° C., 0% RH 5 278.81; 213.99 246.4

The transmission of water vapour through the plastic film and the fibrematerial were measured according to ASTM F 1249-90 using a modulatedinfrared sensor.

Transmission of Water Vapour

Transmission of Area water vapour Sample Test conditions (cm²)(cm³/m²/day) Average 1 23° C., 100% RH 5 45.46; 63.65 54.6

The invention is not limited to the above-described embodiments, but canalso be modified within the scope of the following patent claims.

The chosen materials and method of manufacturing according to theinvention enable a free selection of the shape of the tray. The walls ofthe tray need of course not be straight vis-à-vis its bottom, but mayhave any arbitrary curved shape. The rim need not be parallel with thebottom of the tray, but may be curved.

The trays according to the invention, having a thickness in the order of1 mm, results in, as is apparent from the reported tests, a high loadresistance. Said resistance may of course be increased more by choosinga thicker tray. The manufacturing process using compression-mouldingalso makes it possible to reinforce the tray locally, by for exampledesigning the tray with thicker reinforcement beams, which are formed inconnection with the compression-moulding.

AKD has proven to be a suitable hydrophobing agent. Other hydrophobingagents are however possible. If the tray is to be used for ready-cookeddishes, then a hydrophobing agent that resists both freezing and heatingshould be chosen.

Black PET film gives a high and even lamination temperature. The PETfilm may within the scope of the invention be selected in an arbitrarycolour, and may be provided with a colour-print with text and/orpattern, for example a picture pattern. Other films like PA, PP, PE,PBT, sometimes in combination with EVOH, may also be used depending onend use/customer demands, such as the addition of customer profiles,length of food storage, conditions under which the storage is to takeplace, etc.

In the above-described embodiments, the fibre material is constituted byCTMP. The invention is however not limited to the selection of CTMP.Other fibre materials are possible within the scope of the followingpatent claims.

What is claimed is:
 1. A method of producing a fibre tray, comprisingthe steps of: a) forming a fibre tray by dewatering an aqueoussuspension of cellulose from 1 to 15% in a forming section using adewatering tray, the cellulose comprising at least 75% virginfibre-based mechanical pulp, wherein the 75% virgin fibre-basedmechanical pulp includes at least one of CMP (chemi-mechanical pulp),CTMP (chemithermomechanical pulp), cTMP (CTMP with a lower amount ofadded chemicals relative to CTMP), or HTCTMP (high temperaturechemithermomechanical pulp); b) press-drying the formed tray to a drycontent of 80-95% and a density of 400-650 kg/m3; c) coating the formedtray with a protective barrier; and d) punching or reducing thethickness of a portion of said formed tray.
 2. The method according toclaim 1, wherein said punching or reducing of the thickness of theformed tray is performed at an edge and/or rim portion of the tray. 3.The method of claim 1, wherein said punching or reduction of thethickness of the formed tray is performed by punching or compressingsaid portion of the tray before or after coating with the protectivebarrier.
 4. The method of claim 1, wherein said press-drying isperformed at 250-280° C.
 5. The method of claim 1, wherein saidprotective barrier is applied by coating a surface of the formed traywith a plastic emulsion that is polymerised to a film by the addition ofan initiator, or dries to a film, on the formed tray.
 6. The method ofclaim 1, wherein said protective barrier is constituted by a film,wherein the film includes at least one of PET (polyethyleneterepthalate), PA (polyamide), PP (polypropylene), PE (polyethylene),PBT (polybutylene terepthalate), or EVOH (ethylene vinyl alcoholcopolymer).
 7. The method of claim 1, further comprising a step of heatlaminating said protective barrier to the formed tray.
 8. The method ofclaim 1, wherein said protective barrier is removable from the formedtray by hand force.
 9. The method of claim 1, further comprisingtreating the fibre material of the formed tray with a hydrophobingagent.
 10. The method of claim 9, wherein the hydrophobing agentincludes at least one of AKD (alkyl ketene dimer) and ASA (alkylsuccinic anhydride).
 11. The method of claim 1, wherein the suspensionof cellulose has a pH between 6 and 8.5.